@phdezra , I believe Derby Professional are just the single-edged version of Derby Extra. They’re for barber razors - usually an item used by professionals even though they’re popular amongst shave nerds, too.
I use Derby Extra for a variety of reasons (forgiving and not as sharp for a beginner). They are made in Turkey; see photo.Looking at the Amazon listing for the Derby Premiums, it looks like they are made from Swedish steel, but not in Sweden. All varieties of Derby are made in Turkey.
I haven't tried other grades of Derby, just these Premiums (which I bought August 2019). Yesterday's shave, with a new Futur also used a new Derby blade. I'd call it closer by a smidgen than the Fatboy shave I started this thread with, but with more alum block and AS feedback.
I’m very curious to try Derby Premium (which comes from factory as Single Edge OR Double Edge). This is the one of Swedish steel, regardless of country mfr. Stay tuned!